This proposal is concerned with the establishment of a new methodology for the measurement of the rate of protein synthesis in man using N15 as a tracer. The method will be used to investigate the metabolic alterations due to trauma and the effects of hormones such as insulin, thyroxine ACTH and steroids on protein metabolism. We are also proposing to develop methods for looking at the metabolic inter-relationships of amino acids in man following the administration of N15 labelled amino acid.